A spiroketal derivative having a certain structure is known as being useful for preventing or treating diabetes (refer to Patent Documents 1 to 4). For example, WO 2006/080421 A1 (Patent Document 1) discloses a compound represented by Formula (A):

and use thereof as an anti-diabetes drug.
Patent Document 1 also discloses a process for preparing the compound represented by Formula (A). Scheme 3 (page 24 of Patent Document 1) indicates a preparation process, in which a dibromobenzene derivative is treated with an alkyllithium reagent followed by coupling with a lactone, and after conversion to a tin compound a coupling reaction in the presence of a palladium catalyst is carried out to give the desired compound.
Further, WO 2007/140191 A2 (Patent Document 2) and US patent application publication corresponding thereto: US 2007/0275907 A1 (Patent Document 3) disclose a preparation process in Scheme 4 (pages 24 and 25 and FIG. 4 of Patent Document 2), in which a dihalotoluene derivative is treated with n-BuLi, s-BuLi, t-BuLi, Mg or the like followed by coupling with a lactone, and a tin compound obtained after several steps is subjected to coupling with a benzyl halide derivative to give a desired compound.
Moreover, Patent Document 1 discloses a compound represented by Formula (B):

with stating that the compound has an excellent inhibitory activity against SGLT2.